# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: SS61 course to steer
From: Dan Hogan
Date: 2000 Apr 07, 19:22 EDT

```On 7 Apr 2000, at 7:19, Patrick McVey wrote:
> On leg 61 departing Rio. On the question of Course To Steer.
> 1) Correct me if I'm wrong: This is the course one would steer which
> accounts for tidal stream, .6 knots drift at 185d set. Correct. THEN,
> one applies the magnetic variation & compass deviation. I can get the
> CTS but I don't know if one adds the compass corrections.
It's:
T(ure Course)
V(ariation +/-)
M(agnetic Course)
D(evation +/-)
C(ompass Course)
Add easterly variation/deviation when un-correcting (True-to-
Compass)
Subtract easterly variation/deviation when correcting (Compass
Course-to-True)
> 2) I am using a graphic method for solving tidal stream. Can someone
> point me to a mathematical formula. I didn't readily see one in the
> 4mulas zip file.
To do it mathematically is a kind of long explanation. Most
Navigation manuals call it the current triangle and explain it with
graphic vectors. Bowditch explaines current using vectors.
It is explained in The Calculator Afloat, by Shufeldt/Newcomer,
Naval Institute Press, 1980, ISBN 0-87021-116-1.
Also, most computer DR programs have it built in. Chechk out the
free ones at the Nav-L web site.
> Thanks for the input. Its good to be back after some absence. Thanks
> to the group members for this tremendous resource. Patrick
>
Dan Hogan
dhhogan@XXX.XXX
NAV-L Web Page: http://nav.cnchost.com
```
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